As a community, Tumblr encourages reblogging, as long as everything’s properly credited to the right source. Because of this, we can’t remove properly-credited reblogs of content that you’ve publicly posted on Tumblr.
Tumblr’s Terms of Service (http://www.tumblr.com/policy/en/terms_of_service) state in Section 6 that you as a Tumblr subscriber:
"hereby grants and agrees to grant Tumblr a non-exclusive, worldwide, royalty-free, transferable right and license (with the right to sublicense), to use, copy, cache, publish, display, distribute, modify, create derivative works and store such Subscriber Content and to allow others to do so (“Content License”) in order to provide the Services."
What we mean by this is that properly-credited reblogs of your content may remain on Tumblr even if you delete your original post or earlier reblog. We do this because in order for everyone to feel comfortable with properly-credited reblogging and sharing, our users need to feel confident that their reblogs will not be removed at a later date.
If you feel that the people who reblogged your work failed to give you adequate credit or somehow violated the law or Tumblr policy, send us an e-mail with specific examples of these violations. Otherwise, we won’t be able to remove the reblogs.
*** So if I understand correctly. Tumblr is designed for the person who reblogs, not in favour of the original artist..?